Compared with the traditional explosive blasting method, the silent cracking method has the advantages of safety, no vibration, no flying rock, no noise, no dust and no smoke, etc. It has been widely used and attracted attention all over the world. In the prior art, most of the available silent cracking agents were prepared with quicklime as the main ingredient. In general, the quicklime was milled and mixed with other inorganic materials, such as anhydrous sodium sulphate, alumina cement, etc. in a certain proportion which used to inhibit the hydrate reaction of the quicklime. The mixture is mixed with water when used. Japanese patent application JP56-67059 disclosed a silent cracking agent prepared by milling the quicklime to powder and then mixed with other milled agents which inhibit the hydrate reaction of the quicklime. When used, the mixture is first mixed with water in a certain proportion to form a thick liquid, then the thick liquid is used to fill the boreholes. The defect of this silent cracking agent was inconvenience because it was in the thick liquid state. It has narrow ranges of applied temperature and fields, a high accident rate of holes bursting, low expansion pressure, long cracking time and high consumption of inhibitors. Japanese patent application JP60-80662 also disclosed a silent cracking agent prepared by mixing quicklime as the expansive ingredient with other auxiliary agents forming a product in cubic shape and then reacting with water. Said silent cracking agent had convenience but still had the defects of low expansion pressure, long cracking time and high consumption of inhibitors. Also known is a powder product silent cracking agent produced by adding ferric oxide, potassium fluoride and silicate, etc., to the quicklime, then calcining the mixture in a high temperature furnace at about 1200.degree. to about 1500.degree. C. and then milling. The products produced in this way still had the defects mentioned above. In addition, energy consumption was high during the manufacturing process.
Asahi Chemical Industry Co., Ltd., developed a silent cracking agent which produces an expansion pressure as high as from about 90 to about 100 MPa and having a minimum cracking time of 5 minutes. This silent cracking agent contained expensive organic materials as the expansive auxiliary agent as well as thermosensitive agents. Heating by electric current was necessary in order to decrease the cracking time and increase the expansion pressure of said silent cracking agent. So this agent was complicated in operation and high in cost.